1. Field of the Invention
The present invention relates to a torque limiting power transmission, and more specifically, to a mechanism for a power transmission suitable for use in compressors and other industrial equipment.
2. Description of Related Art
FIGS. 19 and 20 depict a known power transmission as described in JP-A-8-135752. Referring to FIG. 20, an inner lace of ball bearing 24 is fixed to inner cylindrical projecting portion 22A of front housing 22 of compressor 21. Rotor 25 is fixed to an outer race of ball bearing 24. Pulley 26 is fixed to rotor 25, and a first holding member 28 is fixed to pulley 26 by rivets 27. Hub 29 is fixed to shaft 23 of compressor 21 via nut 30. A second holding member 32 is fixed to hub 29 by rivets 31. An elastic ring 33 made from a synthetic resin, or rubber is press-fitted between first holding member 28 and second holding member 32.
Referring to FIG. 19, elastic ring 33 is formed in the shape of a petal, and a plurality of convex portions 33A and concave portions 33B are formed on inner and outer peripheries of elastic ring 33, respectively. A plurality of concave portions 28A and convex portions 28B are formed on a periphery of first holding member 28 corresponding to the plurality of convex portions 33A and concave portions 33B of elastic ring 33. A plurality of concave portions 32A and convex portions 32B are formed on an inner periphery of second holding member 32 corresponding to the plurality of convex portions 33A and concave portions 33B of elastic ring 33.
When a torque is transmitted from pulley 26 to shaft 23 of compressor 21, the respective convex portions 33A and concave portions 33B of elastic ring 33 deform due to compression of the respective concave portions 28A and convex portions 28H of first holding member 28, and the respective concave portions 32A and convex portions 32B of second holding member 32. Thus, the torque is transmitted by a reactive force. When an excessive torque relative to a preset value is generated by, for example, a seizure of compressor 21, elastic ring 33 deforms, decreasing its thickness in the radial direction. As a result, elastic ring 33 slips against concave portions 32A and convex portions 32B of second holding member 32, interrupting the transmission of the torque.
In such a known power transmission, because a plurality of concave portions and convex portions are provided along a radial axis of the first and second holding members respectively, even if the elastic ring slips, causing its convex portions and concave portions to escape from the concave portions and convex portions of the second holding member with which they were originally fitted, they may be re-fitted to the adjacent concave portions and convex portions of the second holding member, and the torque may be transmitted again.
Further, in such a known power transmission, because the elastic modulus of the elastic ring varies depending on the temperature of an area along a radial axis of the first and second holding members, respectively, the torque limiter may become unstable.
It is an object of the present invention to provide a stable power transmission, which may be unaffected by variation of the temperature of an area along a radial axis of the first and second holding members. It is another object of the present invention to provide a stable power transmission. It is yet another object of the present invention to prevent foreign material from entering the transmission. It is still another object of the present invention to prevent abrasion and rust. It is a further object of the present invention to maintain a torque interrupted condition once a torque is interrupted.
According to one embodiment of the invention, a power transmission has a drive side rotatable member having a plurality of tapered radial concave portions with each having a pair of tapered surfaces. The plurality of tapered radial concave portions are disposed in a radial direction along a radial axis of the drive side rotatable member. A driven side rotatable member is connected to a rotary shaft and has a plurality of radial and axial concave portions disposed in a radial direction along a radial axis of the driven side rotatable member. A plurality of balls are each moveable between each of the plurality of tapered radial concave portions and each of the plurality of radial and axial concave portions. A spring is provided on the driven side rotatable member. Further, a ring having an inclined surface is urged by the spring, whereby the ring presses each of the plurality of balls at a point at which the inclined surface is formed. The ring presses each of the plurality of balls to each of the plurality of tapered radial concave portions and to the driven side rotatable member when torque is transmitted. Further, the ring presses each of the plurality of balls to each of the pairs of tapered surfaces of each of the plurality of tapered radial concave portions and to the inclined surface of the ball pressing ring in order to move each of the balls into each of the plurality of radial and axial concave portions when a torque is interrupted. Accordingly, the present invention has a structure which may maintain torque in an interrupted condition once torque is interrupted.
Further, the driven side rotatable member may have an axial interior concave portion connected to each of the plurality of radial and axial concave portions, such that when torque is interrupted, each of the plurality of balls moves into the axial interior concave portion each of the plurality of radial and axial concave portions, thereby preventing each of the plurality of balls from moving radially.
In yet another embodiment, the drive side rotatable member may include a pulley, an outer ring fixed to the pulley, an inner ring pressing against each of the plurality of balls, and an elastic rubber member connecting the outer ring and the inner ring.
In a still another embodiment, the spring may be a belleville spring. An urging force of such a belleville spring presses against the ball pressing ring. The urging force may be adjusted by means of an adjusting screw.
In a further embodiment, a first seal member may provide a seal between an inner peripheral surface of the drive side rotatable member and a peripheral surface of the driven side rotatable member. A second seal member may provide a seal between the inner peripheral surface of the drive side rotatable member and a peripheral surface of the ball pressing ring, thereby forming an enclosed space.
In still a further embodiment, an enclosed area may be formed between a rubber member and the driven side rotatable member by creating a seal between an inner peripheral surface of the rubber member and a peripheral surface of the driven side rotatable member. An enclosed area also may be formed between a rubber member and the ball pressing ring by creating a seal between the inner peripheral surface of the rubber member and a peripheral surface of the ball pressing ring.
Further, an enclosed area may be formed between a ring-like seal member-fixed to the inner ring and the driven side rotatable member by creating a seal between the ring-like seal member-fixed to the inner ring and a peripheral surface of the driven side rotatable member and an enclosed area may be formed between between the rubber member and the ball pressing ring by creating a seal between an inner peripheral surface of the rubber member and a peripheral surface of the ball pressing ring.
In yet a further embodiment, an enclosed area may be formed between the rubber member and the driven side rotatable member by creating a seal between an inner peripheral surface of the rubber member and an enclosed area may be formed between the driven side rotatable member and a ring-like seal member-fixed to the inner ring by providing a seal between a peripheral surface of the driven side rotatable member and the ring-like seal member-fixed to the inner ring and a peripheral surface of the ball pressing ring. A preservative or lubricant may be filled in the enclosed area.
A gap also may be formed between the outer ring and the pulley, such that the enclosed area may be maintained even if the outer ring, the rubber member, and the inner ring are moved toward the pulley. Alternatively, a gap may be formed between the driven side rotatable member and the rotary shaft, such that the enclosed area may be maintained even if the driven side rotatable member, the plurality of balls, and the ball pressing ring are moved toward the pulley. Moreover, a gap may be formed between the driven side rotatable member and the ball pressing ring, such that an urging force of the spring acts upon each of the plurality of balls via the ball pressing ring even when each of the plurality of balls moves into the axial interior concave during a torque interruption.
Further, the inclined surface of the ball pressing ring may have an upper surface and a lower surface. The upper surface. may press against each of the plurality of balls before each of the plurality of balls is moved from each of the plurality of tapered radial concave portions to each of the plurality of radial and axial concave portions by each of the pairs of tapered surfaces of each of the plurality of tapered radial concave portions. Moreover, the lower surface may press against each of the plurality of balls after each of the plurality of balls is moved from each of the plurality of tapered radial concave portions to each of the plurality of radial and axial concave portions by each of the pairs of tapered surfaces of each of the plurality of tapered radial concave portions. In addition, an inclined angle of the lower surface may be less than an inclined angle of the upper surface.
In addition, a first torque may be generated when each of the plurality of balls begins to be moved from each of the plurality of tapered radial concave portions to each of the plurality of radial and axial concave portions by each of the pairs of tapered surfaces of each of the plurality of tapered radial concave portions. This first torque may be substantially equivalent to a second torque, which may be generated when each of the plurality of balls no longer presses against each of the one pairs of tapered surfaces of each of the plurality of tapered radial concaves. Moreover, a depth of the axial interior concave may be selected, such that an urging force of the spring acts upon each of the plurality of balls via the ball pressing ring even when each of the plurality of balls moves into the axial interior concave during a torque interruption.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings.